1. Field of the Invention
The invention relates to an apparatus for increasing the efficiency of fractional distillation trays. The invention more specifically relates to an apparatus providing a higher efficiency multiple downcomer fractionation tray.
2. Related Art
Multiple downcomer fractionation trays were introduced by U.S. Pat. No. 3,410,540 issued to W. Bruckert. This reference describes the characteristic arrangement of a multiple downcomer tray which includes long narrow trough-like downcomers spread across the tray with long rectangular areas of tray decking separating the downcomers. The traditional rectangular shape of the downcomers and the transverse arrangement of downcomers on vertically adjacent trays is also shown.
Multiple downcomer trays are noted for their high capacity. They were therefore Included in an article entitled xe2x80x9cHigh-Capacity Distillationxe2x80x9d published at page 53 of the August 1998 edition of Hydrocarbon Processing and in an article starting at page 23 of the January 1999 edition of Chemical Engineering Process. These article show the trarsverse arrangement of the downcomers on vertically adjacent trays and describe the flow of vapor and liquid through fractionation columns employing the trays.
U.S. Pat. No. 4,159,291 issued to W. Bruckert et al describes alternative structures for the liquid discharge spout openings in the bottom of multiple downcomer fractionation trays. These include inclined wall segments under the spout openings which impart a horizontal velocity component to the liquid exiting the downcomers. This directs liquid laterally (perpendicular to the downcomer) as opposed to the subject invention which directs liquid axially beyond the ends of the downcomer. The apparatus of this reference would not appear to be able to increase the discharge of liquid onto the crescent-shaped section of tray decking adjacent to the wall of the enclosing fractionation column.
Liquid which falls from the bottom of a downcomer of a multiple downcomer tray will fall onto the active vapor-liquid contacting area of the next lower tray. Therefore the area under the downcomer may be employed to perform vapor-liquid contacting. It has been recognized in the art that the liquid falling on the decking could penetrate the decking thus bypassing the intended vapor-liquid contacting. U.S. Pat. No. 5,209,875 introduced the use of antipenetration pans suspended between the trays to reconcile this problem. The antipenetration pans are located under the liquid outlets of the upper tray and oriented perpendicular to the downcomers of the lower tray. Liquid exiting the downcomers falls upon the pans and then flows onto the decking of the lower tray.
The invention is a novel apparatus designed to increase the efficiency of fractionation columns which contain multiple downcomer fractionation trays. The apparatus comprises a liquid distribution pan suspended between vertically adjacent trays which are mounted transverse to each other. The distribution pan collects liquid emanating from the terminal portion of the downcomer of the upper tray and then discharges onto a desired point or area of the active decking area of the next lower tray. The liquid falls upon the lower tray at a more uniform distance from the outlet downcomer of the lower tray, and the liquid has a more uniform residence time upon the tray, thus increasing the separation efficiency of the tray.
One broad embodiment of the invention may be characterized as a tray for performing fractional distillation in a vertical enclosed fractionation column, the tray having at least one trough-like downcomer extending across a central portion of the decking area of the tray, with the tray comprising a downcomer liquid distributor secured to the tray or the next lower tray at a location below openings in the bottom of each terminal portion of the downcomer, said liquid distributor comprising means for intercepting liquid falling from openings in the bottom of the terminal portion of the downcomer and discharging the intercepted liquid beyond the associated end of the downcomer.